The present invention relates to a method for the equalization of particles to be deposited and/or spread upon a moving surface. Equalization is according to a rated density distribution in a particle mass stream in a direction transverse to movement of the mass stream. A device for the application of the method includes means for controlling the volume of the particle mass stream to be deposited depending on a rated density distribution in the stream across its spread width, especially a chip mass stream used in the manufacture of chip boards, particle boards, and the like.
In the production of masses consisting of particles for compacting into boards, the particles already mixed with bonding agents are deposited upon a base surface. The quality of the boards produced by the compacting process depends to a large degree upon a uniform density of the deposited particle mass over the base surface. In this respect it is of no consequence whether the bonding agent mixed with the particles to produce the mass is urea type glue, cement or gypsum.
The particle material may also consist of wood chips of normal dimensions, as needed for manufacturing of chip boards or it may consist of larger surface particles such as wafers and strands or it may consist of a mixture of such chips and wood fibers. The particles to be deposited may also be synthetic granules.
DE-PS No. 1 133 532 makes known a means for forming a particle stream of constant thickness especially wood particles such as chips mixed with bonding agents to form a furnish. Several sensing devices are provided at locations before portioning which are distributed over the width of a conveyor belt with respect to the direction of belt advancement.
When a given height of particle mass exceeds the nominal height, control devices are activated with respect to a distribution device that equalizes the uneven heights of deposited particle mass across the conveyor width. Such a device can only be applied if, before the portioning procedure, there is a large amount of material available as compensatory material to compensate for the equalization of the material to be spread. Accordingly, newly arriving and to be proportioned material is being mixed with already available material. The result is that the material actually used consists of particles that were furnished with bonding agents at different times. For instance particles that were in contact with cement, and in addition have been moistened, and as a result have experienced curing of the cement, will be brought together with particles that were freshly mixed with cement as a bonding agent.
The influence of such a particle mixture upon the strength of the board produced is detrimental. The results are obvious, namely particles already furnished and thereby coated with cured bonding agents cannot bond further with particles that were freshly coated with bonding agents. Hence, despite equal density in the deposited mass the finished boards become scrap because of flawed bonding. This disadvantage of the state of technology demonstrated in the example of a board with cement bonding applies also to chip boards of the type explained above and to particle boards the bonding of which is accomplished with gypsum or to boards made of granules.
In DE-PS No. 947 640 a method and means is disclosed for the manufacture of particleboards, chip boards and the like wherein the particle or chip material is deposited upon roller or belt conveyors, grids or similar means including sheet metal covers which may be attached thereto. The resulting particle mass after scraping off excess material before or after precompression is subjected to continuous and automatic weight control by means of height adjustment of the scraper. The adjustment is made in accordance with indications by a weighing scale to achieve manufactured boards of equal weight.
This method also uses an excess amount of particles whereby, depending on the weight of the particle mass after spreading, some particles must be removed in order to achieve equal weight. Besides destroying the surface of the evenly spread particle mass as a result of this interference, the same disadvantages occur as mentioned above regarding the current state of the art. Also an even distribution of density cannot be achieved in this manner if mixed materials are used, such as particles of different kinds of wood or wood particles mixed with granules. This is so because of the different specific weights in the particle mixture and also as the result of minor variations in the wood mixture. For example, wood particles of higher specific gravity and granules of synthetic material of low specific gravity will necessarily combine over the total spread of deposited mass thereby resulting in a nonuniform density distribution.